Your link to the Jakut article holds what I would consider fairly strong evidence. The article (all emphasis mine) specifies that by
features, as well as by their language, the Jakuts belong to the Tiursk nationalities.
We can look to the wiki article on the Jakuts and find that
The Yakut language belongs to the Siberian branch of the Turkic languages.
Another older work, The Polar World: a Popular Description of Man and Nature in the Arctic and Antarctic Regions of the Globe
By Georg Hartwig, published in 1859, has a chapter on the Jakuts. This also mentions this language connection to the Turkic people:
Though of a Mongolian physiognomy their language which is said to be
intelligible at Constantinople distinctly points to a Turk extraction
and their traditions speak of their original seats as situated on the
Baikal and Angora whence retreating before more powerful hordes they
advanced to the Lena where in their turn they dispossessed the weaker
tribes which they found in possession of the country.
Considering the language connection, and the use of the term nationalities indicating something more widespread than a single tribe, I would conclude the term was indicating a Turkic peoples.